- If Maria in the Leave, In Water and Rebirth endings, he rejects her and this causes her to transform.
- If "Mary" in the Maria ending, she blames him for her death and proceeds to attack James, initiating the final boss fight. However, it is ambiguous if this truly is "Mary".
She appears as a version of Mary's corpse displayed in a metal frame, similar to the Flesh Lip. Her arms and legs end in a series of short tentacles rather than hands or feet, and she is suspended in the metal frame, screaming and upside-down.
Mary attacks by spewing forth a swarm of moths from her mouth in order to injure and delay James, as the insects are flesh-eaters. She can also hit James with the frame she rests in or use her tentacle to strangle him, provided that he is within range.
She takes quite a bit of damage before falling, so saving up ammunition for the encounter would be recommended, though it is not necessary; she eventually falls herself. It is very difficult to attack her with a melee weapon due to the metal frame and tentacles she uses. The rifle is the best choice to fight her with. After she falls to the ground, she whispers James's name repeatedly. One last blow to the now-helpless monster ends the fight.
According to the Book of Lost Memories, Mary's form represents James's conflicted emotions towards her during her final days: Mary's overwhelming feelings of angst, anger, rage, sorrow, pain, loneliness, disgust of her body due to her disease, etc. As Mary said in her letter, "When I first learned that I was... going to die... I didn't want to accept it." The metal lattice probably symbolizes Mary's sense of confinement in being bedridden due to her illness. Ironically, Mary can also use the tentacle to strangle James, similar to his asphyxiation of her.
The moths that surround her are used to symbolize death, a motif in the game:
- Comparatively, Maria has a butterfly tattoo on her abdomen, which represents rebirth.
- James once attempted to give Mary some flowers, but she rejected them. It is known that moths are attracted to flowers and devour them, so the moths may be symbolic of Mary rejecting James's kindness.
- In the Observation Deck, a quote from Job 13:28 can be found on a wall saying, "While I am decaying like a rotten thing, Like a garment that is moth-eaten." This likely a reference to Mary's disease.
- Moths can also be found in the Wood Side Apartments and are attracted to James's flashlight. Before this, James found the flashlight on a mannequin wearing Mary's dress.
- Depending on the ending, Maria or "Mary" says something different before transforming.
- In the Leave ending, Maria says, "No! I won't let you! You deserve to die, James!"
- In the Maria ending, "Mary" says, "James, do you really think I could ever forgive you for what you did?!"
- In the In Water ending, Maria says, "I'll never let you have your MARY back!"
- In the Rebirth ending, Maria says, "Oh James... C'mon James! You must be joking!"
- If James stands in a certain spot, it may be possible for Mary to die without attacking James. However, this may not be possible in all versions of the game.
- Mary's glitch-like transition is visually similar to videotape distortions.
- Mary has some kind of triangular hood appearing during her transformation process.
- Defeating Mary in the Silent Hill HD Collection awards the trophy/achievement "Say Goodbye".
- Mary is one of the only five monsters that are conscious and can speak in their monstrous forms, the other four being Leonard Wolf, Momma, Steel Guardian, and Monocle Man. Note that the Sad Daddy could speak only in its human manifestation.
- Mary makes a cameo in Silent Hill: Shattered Memories. She can be seen floating in the corner of Dr. Kaufmann's office during the UFO ending.
- Unlike in other games, James doesn't jump in a hole or goes downstairs to start the final battle. Instead he ascends from the basement to the first floor to fight the Pyramid Heads and then higher to meet Mary.